The cooling of high power electronic modules carried on a circuit board has always been a troublesome problem. It is possible to use a liquid coolant pumped through pipes in contact with a heat sink to remove the heat they generate. However, such an approach requires relatively complex tubing and the expense of an external chiller to accept the heat carried by the coolant. It is therefore desirable to use ambient air to cool these modules. Because the high heat generation of such modules makes free convective cooling insufficient, forced convective cooling is necessary.
Forced convective cooling has the advantages of simplicity and cost effectiveness. Because of the typical layout of circuit boards and the modules carried by them, the usual procedure is to introduce air at one edge of the circuit board and force it across the many modules carried on the board to cool them. However, the air which passes near the first modules is heated, lessening its ability to cool those modules which it encounters later as it flows around them. Therefore, there have been attempts made to implement so-called "parallel" cooling or air flow, where air is distributed to the modules involved before it has been warmed by any other of the modules. These designs, however, cannot always transfer enough heat to the air passing by them to keep the temperature of the module within the safe region.